CN111183544B - Gel polymer electrolyte composition and lithium secondary battery including the same - Google Patents
Gel polymer electrolyte composition and lithium secondary battery including the same Download PDFInfo
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- CN111183544B CN111183544B CN201880051077.8A CN201880051077A CN111183544B CN 111183544 B CN111183544 B CN 111183544B CN 201880051077 A CN201880051077 A CN 201880051077A CN 111183544 B CN111183544 B CN 111183544B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0565—Polymeric materials, e.g. gel-type or solid-type
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0567—Liquid materials characterised by the additives
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
- H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0025—Organic electrolyte
- H01M2300/0028—Organic electrolyte characterised by the solvent
- H01M2300/0034—Fluorinated solvents
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0025—Organic electrolyte
- H01M2300/0045—Room temperature molten salts comprising at least one organic ion
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0085—Immobilising or gelification of electrolyte
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The present invention relates to a gel polymer electrolyte composition for a lithium secondary battery, a gel polymer electrolyte prepared by polymerizing the gel polymer electrolyte composition, and a secondary battery including the gel polymer electrolyte, and in particular, to a gel polymer electrolyte composition for a lithium secondary battery including a lithium salt, a non-aqueous organic solvent, an ionic liquid, an oligomer having a specific structure, a flame retardant, and a polymerization initiator; a gel polymer electrolyte formed by polymerizing the gel polymer electrolyte composition in an inert atmosphere; and a lithium secondary battery having improved flame retardancy and high-temperature stability by including the gel polymer electrolyte.
Description
Technical Field
Cross Reference to Related Applications
The present application claims the benefits of korean patent application No. 2017-0164111 filed in the korean intellectual property office on 1 of 12 months in 2017 and korean patent application No. 2018-0151894 filed in the korean intellectual property office on 30 of 11 months in 2018, the disclosures of which are incorporated herein by reference in their entirety.
Technical Field
The present invention relates to a gel polymer electrolyte composition and a lithium secondary battery including the same.
Background
As the demand for portable electronic devices has rapidly increased, the demand for secondary batteries as an energy source has increased significantly, and among these secondary batteries, lithium secondary batteries having high energy density, high operating potential, long cycle life, and low self-discharge rate have been commercialized and widely used.
Recently, with increasing attention to environmental problems, electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs) that can replace vehicles using fossil fuel, such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, have been studied extensively. Nickel-hydrogen (Ni-MH) secondary batteries are mainly used as power sources for Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs), but researches on using lithium secondary batteries having high energy density, high discharge voltage, and output stability have been actively conducted, and some researches have been commercialized.
The lithium secondary battery has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode is stacked or wound, and is configured by accommodating the electrode assembly in a battery case and injecting a nonaqueous electrolyte solution therein. The charging and discharging of the lithium secondary battery are performed while repeating a process in which lithium ions of the positive electrode are intercalated into and deintercalated from the negative electrode.
As the nonaqueous electrolyte solution, a liquid electrolyte solution including an organic solvent in which an electrolyte salt is dissolved is mainly used. However, the liquid electrolyte solution has disadvantages in that: not only is the possibility of volatilization of the organic solvent high, but also safety is low due to combustion caused by an increase in the ambient temperature and the temperature of the battery itself.
That is, in order to increase the energy density of the lithium secondary battery, it is necessary to increase the driving voltage of the battery, but since the liquid electrolyte solution is oxidized and decomposed under high pressure conditions of 4.3V or more, an unstable film having an uneven composition is formed on the surface of the positive electrode. Since the formed film is not stably maintained during repeated charge and discharge to cause continuous oxidative decomposition of the electrolyte solution, such continuous decomposition reaction forms a thick resistive layer on the surface of the positive electrode and consumes lithium ions and electrons contributing to reversible capacity, which causes a problem of capacity reduction of the positive electrode.
In particular, for a carbonate-based organic solvent used as a main solvent of a liquid electrolyte solution, since its flash point (flash point) is low and volatility is high, the carbonate-based organic solvent easily causes flame reaction when the temperature is increased in the case of misuse of a battery, and serves as a fuel in the combustion reaction of an electrode active material. The combustion reaction between the electrode active material and the electrolyte solution rapidly increases the temperature of the battery to cause a thermal runaway phenomenon.
In order to solve these limitations, a lithium polymer secondary battery has been developed in which a gel polymer electrolyte having excellent electrochemical stability is used instead of a liquid electrolyte solution.
However, the gel polymer electrolyte has disadvantages in that: it not only has lower ionic conductivity than the liquid electrolyte solution, but also is not easy to ensure flame retardancy due to the carbonate-based solvent included in the gel polymer electrolyte.
Accordingly, there is a need to develop a technology capable of preparing a gel polymer electrolyte having improved flame retardancy and oxidation resistance even at high voltage.
Prior art literature
Korean patent application laid-open publication No. 2011-0033106
Disclosure of Invention
Technical problem
One aspect of the present invention provides a gel polymer electrolyte composition for a lithium secondary battery.
Another aspect of the present invention provides a gel polymer electrolyte prepared by polymerizing the gel polymer electrolyte composition for a lithium secondary battery.
Another aspect of the present invention provides a lithium secondary battery having improved high temperature stability by including the gel polymer electrolyte.
Technical proposal
According to one aspect of the present invention, there is provided a gel polymer electrolyte composition for a lithium secondary battery, which includes a lithium salt, a non-aqueous organic solvent, an ionic liquid, an oligomer, a flame retardant, and a polymerization initiator,
wherein the oligomer includes at least one selected from the group consisting of oligomers represented by the following formulas 1 and 2.
[ 1]
In the formula (1) of the present invention,
r is an aliphatic hydrocarbon group or an aromatic hydrocarbon group,
R a 、R b 、R c and R d Each independently is a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms,
R e is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms,
r 'and R' are each independently hydrogen, or alkyl having 1 to 3 carbon atoms,
a is an integer of one of 1 to 3,
b is an integer of one of 0 to 2,
n, m and x are the number of repeating units,
n is an integer of one of 1 to 10,
m is an integer of one of 1 to 5, and
x is an integer from 1 to 15.
[ 2]
In the formula (2) of the present invention,
R f an alkylene radical having 1 to 5 carbon atoms which is unsubstituted or substituted by at least one fluorine,
R g 、R h 、R i and R j Each independently is a fluorine element, or a fluorine substituted or unsubstituted alkyl group having 1 to 3 carbon atoms,
R 0 is an aliphatic hydrocarbon group or an aromatic hydrocarbon group,
R' "is hydrogen, or an alkyl group having 1 to 3 carbon atoms,
o is an integer of one of 1 to 3,
p and q are the number of repeating units,
p is an integer of one of 1 to 10, and
q is an integer from 1 to 15.
The ionic liquid may comprise a compound selected from the group consisting of BF 4 - 、PF 6 - 、ClO 4 - Bis (fluorosulfonyl) imide (N (SO) 2 F) 2 - The method comprises the steps of carrying out a first treatment on the surface of the FSI), (bis) trifluoromethanesulfonyl imide (N (SO) 2 CF 3 ) 2 - TFSI), bis-perfluoroethanesulfonyl imide (N (SO) 2 C 2 F 5 ) 2 - BETI), and oxalyldifluoroborate (BF 2 (C 2 O 4 ) - ODFB) as an anionic component, and may include at least one selected from the group consisting of cations represented by formulas 3 to 7 as a cationic component.
[ 3]
In the case of the method of 3,
R 1 、R 2 、R 3 and R is 4 Each independently is hydrogen, or an alkyl group having 1 to 5 carbon atoms.
[ 4]
In the case of the method of claim 4,
R 5 and R is 6 Each independently is an alkyl group having 1 to 5 carbon atoms.
[ 5]
In the case of the method of claim 5,
R 7 and R is 8 Each independently is an alkyl group having 1 to 5 carbon atoms.
[ 6]
In the case of the method of 6,
R 9 、R 10 、R 11 and R 12 Each independently is an alkyl group having 1 to 5 carbon atoms.
[ 7]
In the case of the method of step 7,
R 13 、R 14 、R 15 and R 16 Each independently is an alkyl group having 1 to 5 carbon atoms.
The ionic liquid may be included in an amount of 1 to 50 wt% based on the total weight of the gel polymer electrolyte composition for a lithium secondary battery.
Further, the oligomer represented by formula 1 may be an oligomer represented by the following formula 1 a.
[ 1a ]
In the case of the formula (1 a),
n1, m1 and x1 are the number of repeating units,
n1 is an integer of one of 1 to 10,
m1 is an integer of one of 1 to 5, and
x1 is an integer from 1 to 15.
Further, the oligomer represented by formula 2 may be an oligomer represented by the following formula 2 a.
[ 2a ]
In the case of the formula (2 a),
p1 and q1 are the number of repeating units,
p1 is an integer of one of 1 to 10, and
q1 is an integer of one of 1 to 15.
The oligomer may be included in an amount of 0.1 to 30 wt% based on the total weight of the gel polymer electrolyte composition for a lithium secondary battery.
Further, the flame retardant may be a compound represented by the following formula 8.
[ 8]
In the case of the method of 8,
R 17 、R 18 、R 19 、R 20 、R 21 and R 22 Each independently is selected from the group consisting of H, F, -CF 3 、-CF 2 CF 3 、-C(CF 3 ) 3 、-Cl、-CCl 3 、-CF 2 CCl 3 、-C(CCl 3 ) 3 、-Br、-CBr 3 、-CBr 2 CBr 3 、-C(CBr 3 ) 3 、I、-CI 3 、-CI 2 CI 3 and-C (CI) 3 ) 3 One of the groups formed, and
R 17 、R 18 、R 19 、R 20 、R 21 and R 22 In (a) and (b)At least one may include at least one selected from the group consisting of F, cl, br, and I.
The flame retardant may be included in an amount of 1 to 30 wt% based on the total weight of the gel polymer electrolyte composition for a lithium secondary battery.
According to another aspect of the present invention, there is provided a gel polymer electrolyte prepared by polymerizing the gel polymer electrolyte composition of the present invention.
According to another aspect of the present invention, there is provided a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and the gel polymer electrolyte prepared in the present invention.
The positive electrode may include a positive electrode active material represented by the following formula 9.
[ 9]
Li(Ni a1 Co b1 Mn c1 )O 2
In the case of the method of 9,
a1<0.9,0.05< b1<0.17,0.05< c1<0.17, and a1+b1+c1=1.
Advantageous effects
According to the present invention, by further including an oligomer having a specific structure, an ionic liquid, and a flame retardant in a nonaqueous electrolyte solvent in which a lithium salt is dissolved, a composition for a gel polymer electrolyte having improved flame retardancy can be prepared. In addition, by using the composition for a gel polymer electrolyte, a lithium secondary battery including a gel polymer electrolyte having improved high temperature stability can be prepared.
Detailed Description
Hereinafter, the present invention will be described in more detail. In this case, it will be understood that words or terms used in the specification and claims should not be construed as meaning defined in a commonly used dictionary. It is to be further understood that the words or terms should be interpreted to have meanings consistent with the technical idea of the present invention and the meanings in the background of the related technology, based on the principle that the inventor can appropriately define the words or terms to best explain the present invention.
It will be further understood that the terms "comprises," "comprising," "includes," or "having," when used in this specification, specify the presence of stated features, integers, steps, elements, or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, elements, or groups thereof.
In the present specification, the symbol "%" represents% by weight unless explicitly stated otherwise.
Before describing the present invention, the symbols "a" and "b" in the description of "a to b carbon atoms" each represent the number of carbon atoms included in a specific functional group. That is, the functional group may include "a" to "b" carbon atoms. For example, the expression "alkylene group having 1 to 5 carbon atoms" means an alkylene group comprising 1 to 5 carbon atoms, i.e. -CH 2 -、-CH 2 CH 2 -、-CH 2 CH 2 CH 2 -、-CH 2 (CH 2 )CH-、-CH(CH 2 )CH 2 -, and-CH (CH) 2 )CH 2 CH 2 -。
In this case, the expression "alkylene group" means a branched or unbranched aliphatic hydrocarbon group or a functional group in the form in which one hydrogen atom is removed from carbon atoms located at both ends of the aliphatic hydrocarbon group.
Gel polymer electrolyte composition for lithium secondary battery
In particular, in an embodiment of the present invention,
there is provided a gel polymer electrolyte composition for a lithium secondary battery, which includes a lithium salt, a non-aqueous organic solvent, an ionic liquid, an oligomer, a flame retardant, and a polymerization initiator,
Wherein the oligomer is at least one selected from the group consisting of oligomers represented by the following formulas 1 and 2.
[ 1]
In the formula (1) of the present invention,
r is an aliphatic hydrocarbon group or an aromatic hydrocarbon group,
R a 、R b 、R c and R d Each independently is a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms,
R e is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms,
r 'and R' are each independently hydrogen, or alkyl having 1 to 3 carbon atoms,
a is an integer of one of 1 to 3,
b is an integer of one of 0 to 2,
n, m and x are the number of repeating units,
n is an integer of one of 1 to 10,
m is an integer of one of 1 to 5, and
x is an integer from 1 to 15.
[ 2]
In the formula (2) of the present invention,
R f an alkylene radical having 1 to 5 carbon atoms which is unsubstituted or substituted by at least one fluorine,
R g 、R h 、R i and R j Each independently is a fluorine element, or a fluorine substituted or unsubstituted alkyl group having 1 to 3 carbon atoms,
R 0 is an aliphatic hydrocarbon group or an aromatic hydrocarbon group,
r' "is hydrogen, or an alkyl group having 1 to 3 carbon atoms,
o is an integer of one of 1 to 3,
p and q are the number of repeating units,
p is an integer of one of 1 to 10, and
q is an integer from 1 to 15.
(1) Lithium salt
First, in the gel polymer electrolyte composition for a lithium secondary battery of the present invention, any lithium salt commonly used in an electrolyte of a lithium secondary battery may be used as the lithium salt without limitation, and in particular, the lithium salt may include Li + As cations, and may include a cation selected from the group consisting of BF 4 - 、PF 6 - 、ClO 4 - Bis (fluorosulfonyl) imide (N (SO) 2 F) 2 - The method comprises the steps of carrying out a first treatment on the surface of the FSI), (bis) trifluoromethanesulfonyl imide (N (SO) 2 CF 3 ) 2 - TFSI), bis-perfluoroethanesulfonyl imide (N (SO) 2 C 2 F 5 ) 2 - BETI), and oxalyldifluoroborate (BF 2 (C 2 O 4 ) - ODFB) as an anion. In particular, the lithium salt may comprise a material selected from the group consisting of LiBF 4 、LiPF 6 、LiClO 4 、LiN(SO 2 F) 2 、LiN(SO 2 CF 3 ) 2 、LiN(SO 2 C 2 F 5 ) 2 And LiBF 2 (C 2 O 4 ) At least one of the groups being constituted.
The lithium salt may be appropriately changed within a generally usable range, but may be specifically included in the gel polymer electrolyte composition at a concentration of 0.8M to 3M, for example, 1.0M to 2.5M. In the case where the concentration of the lithium salt is more than 3M, the lithium ion transporting effect in the gel polymer electrolyte may be reduced due to the increase in viscosity of the electrolyte.
(2) Nonaqueous organic solvents
Further, in the gel polymer electrolyte composition according to the embodiment of the present invention, the type of the nonaqueous organic solvent is not limited as long as the nonaqueous organic solvent can minimize decomposition caused by oxidation reaction during charge and discharge of the secondary battery and can exhibit desired characteristics together with the additive, and as the nonaqueous organic solvent, a carbonate-based organic solvent, an ether-based organic solvent, or an ester-based organic solvent may be used alone or in a mixture of two or more thereof.
The carbonate-based organic solvent in the organic solvent may include at least one selected from the group consisting of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent. In particular, the cyclic carbonate-based organic solvent may include at least one selected from the group consisting of ethylene carbonate (ethylene carbonate, EC), propylene carbonate (propylene carbonate, PC), 1, 2-butylene carbonate, 2, 3-butylene carbonate, 1, 2-pentene carbonate, 2, 3-pentene carbonate, vinylene carbonate, and fluoroethylene carbonate (FEC), and in particular may include a mixed solvent of ethylene carbonate having a high dielectric constant and propylene carbonate having a relatively lower melting point than ethylene carbonate.
Further, the linear carbonate-based organic solvent, which is a solvent having a low viscosity and a low dielectric constant, may include at least one selected from the group consisting of dimethyl carbonate (dimethyl carbonate, DMC), diethyl carbonate (diethyl carbonate, DEC), dipropyl carbonate, methyl ethyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, and in particular, may include dimethyl carbonate.
As the ether-based organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, and ethylpropyl ether, or a mixture of two or more thereof may be used, but the present invention is not limited thereto.
The ester-based organic solvent may include at least one selected from the group consisting of a linear ester-based organic solvent and a cyclic ester-based organic solvent.
In this case, specific examples of the linear ester-based organic solvent may be any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, or a mixture of two or more thereof, but the present invention is not limited thereto.
Specific examples of the cyclic ester-based organic solvent may be any one selected from the group consisting of γ -butyrolactone, γ -valerolactone, γ -caprolactone, σ -valerolactone, and ε -caprolactone, or a mixture of two or more thereof, but the present invention is not limited thereto.
The high-viscosity cyclic carbonate-based organic solvent can be used as an organic solvent because it has a high dielectric constant to well dissociate lithium salts in an electrolyte. In addition, in order to prepare an electrolyte having higher conductivity, the above-mentioned cyclic carbonate-based organic solvent may be mixed with a low-viscosity, low-dielectric constant linear carbonate-based compound (such as dimethyl carbonate and diethyl carbonate), and a linear ester-based compound in an appropriate ratio and used as an organic solvent.
Specifically, a mixture of a cyclic carbonate-based compound and a linear carbonate-based compound may be used as the organic solvent, and the weight ratio solvent of the cyclic carbonate-based compound and the linear carbonate-based compound in the organic solvent may be in the range of 10:90 to 70:30.
Further, since the gel polymer electrolyte composition for a lithium secondary battery of the present invention can minimize the volatility of an organic solvent and suppress the flame retardancy by including an ionic liquid, an oligomer represented by formulas 1 and 2, and a flame retardant, which will be described later, in a non-aqueous electrolyte solution in which a lithium salt is dissolved, it is possible to prepare a gel polymer electrolyte capable of improving the stability (providing flame retardancy) of a battery.
(3) Ionic liquid
The ionic liquid included in the gel polymer electrolyte composition for a lithium secondary battery of the present invention can improve flame retardancy and high-temperature safety of the gel polymer electrolyte due to high oxidation stability and low possibility of ignition.
The ionic liquid may comprise the same anionic component as the lithium salt selected from the group consisting of BF 4 - 、PF 6 - 、ClO 4 - Bis (fluorosulfonyl) imide (N (SO) 2 F) 2 - The method comprises the steps of carrying out a first treatment on the surface of the FSI), (bis) trifluoromethanesulfonyl imide (N (SO) 2 CF 3 ) 2 - TFSI), bis-perfluoroethanesulfonyl imide (N (SO) 2 C 2 F 5 ) 2 - BETI), and oxalyldifluoroborate (BF 2 (C 2 O 4 ) - ODFB) as an anionic component, and may include at least one selected from the group consisting of cations represented by the following formulas 3 to 7At least one of the groups serves as a cationic component.
[ 3]
In the case of the method of 3,
R 1 、R 2 、R 3 and R is 4 Each independently is hydrogen, or an alkyl group having 1 to 5 carbon atoms.
[ 4]
In the case of the method of claim 4,
R 5 and R is 6 Each independently is an alkyl group having 1 to 5 carbon atoms.
[ 5]
In the case of the method of claim 5,
R 7 and R is 8 Each independently is an alkyl group having 1 to 5 carbon atoms.
[ 6]
In the case of the method of 6,
R 9 、R 10 、R 11 and R 12 Each independently is an alkyl group having 1 to 5 carbon atoms.
[ 7]
In the case of the method of step 7,
R 13 、R 14 、R 15 and R 16 Each independently is an alkyl group having 1 to 5 carbon atoms.
The cation represented by formula 3 may include at least one selected from the group consisting of cations represented by the following formulas 3a and 3 b.
[ 3a ]
[ 3b ]
Further, the cation represented by formula 4 may include at least one selected from the group consisting of compounds represented by the following formulas 4a and 4 b.
[ 4a ]
[ 4b ]
Further, the compound represented by formula 5 may include at least one selected from the group consisting of compounds represented by the following formulas 5a and 5 b.
[ 5a ]
[ 5b ]
In formula 6, R 9 、R 10 、R 11 And R 12 Each independently is an alkyl group having 1 to 3 carbon atoms.
Further, the compound represented by formula 7 may be a compound represented by the following formula 7 a.
[ 7a ]
The ionic liquid may be included in an amount of 1 to 50 wt%, specifically 5 to 40 wt%, and more specifically 10 to 30 wt%, based on the total weight of the gel polymer electrolyte composition for a lithium secondary battery.
When the amount of the ionic liquid is 50 wt% or less, wetting can be ensured by preventing the phenomena of an increase in resistance and a decrease in lithium ion migration by preventing an increase in viscosity of the electrolyte. In particular, since the ionic liquid does not have self-extinguishing properties, the ionic liquid may be mixed with the gel polymer electrolyte composition to provide flame retardancy of the gel polymer electrolyte composition.
When the amount of the ionic liquid is less than 1% by weight, the effect of improving the oxidation safety and flame retardancy may not be significant. In addition, since the ionic liquid has a high viscosity, when the ionic liquid is included at a cosolvent level (for example, greater than 50 wt%), the viscosity of the gel polymer electrolyte composition increases to decrease the wettability of the electrolyte, and thus, it is difficult to function as an electrolyte. In particular, in the case where the amount of the ionic liquid is increased, since the dielectric constant is reduced while the salt concentration in the gel polymer electrolyte composition for a lithium secondary battery is increased, the lithium salt dissociability is reduced, and thus, the lithium salt may not be properly dissolved.
(4) Oligomer
In addition, since the oligomer included in the gel polymer electrolyte composition for a lithium secondary battery of the present invention has the ability to dissociate lithium salts, the oligomer can improve lithium ion mobility, and can be manufactured by specifically controlling the concentration of lithium ions (Li + ) Side reactions of (2) and decomposition of lithium saltsThe reaction suppresses gas generation and ignition during overcharge.
The oligomer may include at least one selected from the oligomers represented by the following formulas 1 and 2.
[ 1]
In the formula (1) of the present invention,
r is an aliphatic hydrocarbon group or an aromatic hydrocarbon group,
R a 、R b 、R c and R d Each independently is a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms,
R e is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms,
r 'and R' are each independently hydrogen, or alkyl having 1 to 3 carbon atoms,
a is an integer of one of 1 to 3,
b is an integer of one of 0 to 2,
n, m and x are the number of repeating units,
n is an integer of one of 1 to 10,
m is an integer of one of 1 to 5, and
x is an integer from 1 to 15.
[ 2]
In the formula (2) of the present invention,
R f an alkylene radical having 1 to 5 carbon atoms which is unsubstituted or substituted by at least one fluorine,
R g 、R h 、R i and R j Each independently is a fluorine element, or a fluorine substituted or unsubstituted alkyl group having 1 to 3 carbon atoms,
R 0 Is an aliphatic hydrocarbon group or an aromatic hydrocarbon group,
r' "is hydrogen, or an alkyl group having 1 to 3 carbon atoms,
o is an integer of one of 1 to 3,
p and q are the number of repeating units,
p is an integer of one of 1 to 10, and
q is an integer from 1 to 15.
Specifically, in formula 1 or formula 2, R or R 0 The aliphatic hydrocarbon group of (a) may include at least one selected from the group consisting of (a) at least one alicyclic hydrocarbon group and (b) at least one straight chain hydrocarbon group, wherein (a) alicyclic hydrocarbon group is selected from the group consisting of: a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms, a substituted or unsubstituted cycloalkenylene group having 4 to 20 carbon atoms, and a substituted or unsubstituted heterocycloalkylene group having 2 to 20 carbon atoms, (b) a linear hydrocarbon group selected from the group consisting of: a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms, a substituted or unsubstituted alkylene group having 2 to 20 carbon atoms, and a substituted or unsubstituted alkynylene group having 2 to 20 carbon atoms.
In addition, R or R 0 The aromatic hydrocarbon group of (c) may include at least one selected from the group consisting of a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, and a substituted or unsubstituted heteroarylene group having 2 to 20 carbon atoms.
Specifically, the oligomer represented by formula 1 may be an oligomer represented by the following formula 1 a.
[ 1a ]
In the case of the formula (1 a),
n1, m1 and x1 are the number of repeating units,
n1 is an integer of one of 1 to 10,
m1 is an integer of one of 1 to 5, and
x1 is an integer from 1 to 15.
Further, the oligomer represented by formula 2 may be an oligomer represented by the following formula 2 a.
[ 2a ]
In the case of the formula (2 a),
p1 and q1 are the number of repeating units,
p1 is an integer of one of 1 to 10, and
q1 is an integer of one of 1 to 15.
The oligomer may be included in an amount of 0.1 to 30 wt%, specifically 0.5 to 20 wt%, and more specifically 1 to 10 wt%, based on the total weight of the gel polymer electrolyte composition for a lithium secondary battery.
If the amount of the oligomer is 0.1 wt% or more, a gel polymer electrolyte having a stable network structure may be prepared, and if the amount of the oligomer is 30 wt% or less, for example, 20 wt% or less, wettability may be ensured by preventing an increase in resistance due to the addition of an excessive amount of the oligomer, and at the same time, ion conductivity may be prevented from decreasing by improving movement restriction of lithium ions.
In the case where the amount of the oligomer is more than 30% by weight, the oligomer is not completely dissolved but remains in the non-aqueous organic solvent, thereby causing an increase in electrical resistance. In particular, since the oligomer has a low dielectric constant, it is difficult for lithium salt to be uniformly dissolved in the gel polymer electrolyte composition when the amount of the oligomer increases, and the ion conductivity may be lowered due to a decrease in lithium ion mobility caused by a dense polymer matrix structure formed after curing.
Furthermore, the weight average molecular weight (Mw) of the oligomer represented by formula 1 or formula 2 may be controlled by the number of repeating units, and may be in the range of about 1,000g/mol to about 100,000g/mol, specifically 1,000g/mol to 50,000g/mol, and more specifically 1,000g/mol to 10,000g/mol. In the case where the weight average molecular weight of the oligomer is within the above range, the formation of the polymer matrix (network) can be promoted to form a stable gel polymer electrolyte. Therefore, by suppressing ignition due to overcharge, the high-temperature durability of the secondary battery can be effectively improved.
In the case where the weight average molecular weight of the oligomer is less than 1,000g/mol, formation of the polymer matrix may be difficult, and the mechanical strength of the gel polymer electrolyte may be lowered. In the case where the weight average molecular weight is more than 100,000g/mol, since the physical properties of the oligomer itself become rigid and the affinity for the electrolyte solvent is reduced, it is difficult to dissolve, and thus, the performance battery of the lithium secondary battery may be deteriorated.
The weight average molecular weight may refer to a standard polystyrene equivalent value measured by gel permeation chromatography (Gel Permeation Chromatography: GPC), and unless otherwise indicated, the molecular weight may refer to the weight average molecular weight. For example, in the present invention, GPC conditions are as follows: the weight average molecular weight was measured by using the 1200 series of Agilent Technologies, in which case a Agilent Technologies PL mixed B column can be used, and Tetrahydrofuran (THF) can be used as the solvent.
Since the oligomer represented by formula 1 or formula 2 is electrochemically stable by exhibiting balanced affinity to a positive electrode or separator (SRS layer) as a hydrophilic portion and a negative electrode or separator fabric as a hydrophobic portion in a secondary battery, the oligomer can contribute to improvement of performance of the lithium secondary battery. That is, the oligomer represented by formula 1 contains a siloxane group (-Si-O-) and a urethane group (-N-C (O) O-) as a hydrophobic moiety and an acrylate group functional group as a hydrophilic moiety capable of forming crosslinks themselves at both ends thereof, and the oligomer represented by formula 2 contains a fluorine-substituted vinyl group as a hydrophobic moiety and an acrylate group functional group as a hydrophilic moiety capable of forming crosslinks themselves at both ends thereof, so that the oligomer represented by formula 1 or formula 2 functions as a surfactant in a battery to be able to reduce the surface resistance of an electrode interface. Accordingly, the electrolyte for a lithium secondary battery including the oligomer represented by formula 1 or formula 2 may have more improved wetting effect.
In addition, since the oligomer represented by formula 1 or formula 2 has an ability to dissociate a lithium salt, the oligomer may improve lithium ion mobility. In particular, since they each contain a fluorine-substituted vinyl group or siloxane group (-Si-O-) having high electrochemical stability and low reactivity with Li ions as a main chain repeating unit, lithium ions (Li + ) Side reactions of (a) and decomposition reaction of lithium salt (salt), whereby the amount of such as CO or CO during overcharge can be reduced 2 And the like. Therefore, by suppressing ignition during overcharge, the stability of the secondary battery can be improved.
Therefore, with the gel polymer electrolyte prepared from the gel polymer electrolyte composition of the present invention including the oligomer represented by formula 1 or formula 2 instead of the polymer having an alkylene oxide skeleton (such as ethylene oxide, propylene oxide, or butylene oxide) or the dialkylsiloxane, fluorosilicone, or the graft polymer and block copolymer having the unit thereof, which have been commercialized during the preparation of the conventional gel polymer electrolyte, since side reactions with the electrode are reduced, the effect of stabilizing the interface between the electrode and the electrolyte can be achieved.
(5) Flame retardant
In addition, the flame retardant included in the gel polymer electrolyte composition for a lithium secondary battery of the present invention can provide flame retardancy to the gel polymer electrolyte composition and the gel polymer electrolyte prepared therefrom by inhibiting the combustion reaction of the electrode material and the gel polymer electrolyte composition.
The flame retardant may be a compound represented by the following formula 8.
[ 8]
In the case of the method of 8,
R 17 、R 18 、R 19 、R 20 、R 21 and R 22 Each independently isSelected from H, F, -CF 3 、-CF 2 CF 3 、-C(CF 3 ) 3 、-Cl、-CCl 3 、-CF 2 CCl 3 、-C(CF 3 ) 3 、-Br、-CBr 3 、-CBr 2 CBr 3 、-C(CBr 3 ) 3 、I、-CI 3 、-CI 2 CI 3 and-C (CI) 3 ) 3 One of the groups formed, and
R 17 、R 18 、R 19 、R 20 、R 21 and R 22 May include at least one selected from the group consisting of F, cl, br, and I.
Oxygen present in the cell is a determining factor in reducing the gel conversion of monomers and/or oligomers during gelation. That is, since radicals (radials) generated by the polymerization initiator are easily reacted with oxygen and consumed, the polymerization reactivity of gelation is reduced in the presence of oxygen.
In addition, the positive electrode of the lithium secondary battery is structurally unstable in an overcharged state, wherein such an unstable positive electrode structure is easily collapsed and releases oxygen radicals during exposure to high temperatures, and the generated oxygen radicals react exothermically with the electrolyte to cause thermal runaway of the battery. Further, since oxygen radicals generate ethylene gas or the like by reacting with an electrolyte and oxygen gas is generated in the battery, the oxygen radicals cause ignition and explosion of the lithium secondary battery.
In this case, since the compound represented by formula 8 included as a flame retardant includes a resonance structure and at least one halogen element as substituents, the compound represented by formula 8 can achieve an effect of suppressing combustion by preventing oxygen radical propagation (O radical propagation) that occurs explosively during combustion.
Specifically, the compound represented by formula 8 may be at least one selected from the group consisting of compounds represented by the following formulas 8a to 8 d.
[ 8a ]
[ 8b ]
[ 8c ]
[ 8d ]
The flame retardant may be included in an amount of 1 to 30 wt%, specifically 5 to 25 wt%, more specifically 10 to 20 wt%, based on the total weight of the gel polymer electrolyte composition for a lithium secondary battery.
In the case where the amount of the flame retardant is less than 1% by weight, the effect of improving the incombustibility and the flame retardancy may not be significant. If the amount of the flame retardant is 30 wt% or less, since the dielectric constant of the electrolyte can be maintained at an appropriately high level, an increase in resistance due to a decrease in the degree of dissociation of the lithium salt is prevented, and thus, a decrease in ion conductivity can be prevented by improving the movement restriction of lithium ions.
In the case where the amount of the flame retardant is more than 30% by weight, since the flame retardant increases the viscosity of the gel polymer electrolyte composition as a factor of reducing ion mobility, the performance (high rate performance) of the battery may be deteriorated. In addition, since the flame retardant in the gel polymer electrolyte composition has low polarity to have a low dielectric constant value, when an excessive amount of the flame retardant is included in the electrolyte, the lithium salt dissociation ability may be reduced, and thus, the lithium salt may not be properly dissolved.
(6) Polymerization initiator
In addition, the gel polymer electrolyte composition of the present invention may include a conventional polymerization initiator capable of generating radicals by heat and light.
An azo-based polymerization initiator or a peroxide-based polymerization initiator may be used as the above-described polymerization initiator, and representative examples of the polymerization initiator may be: at least one peroxide group selected from the group consisting of benzoyl peroxide (benzoyl peroxide), acetyl peroxide (acetyl peroxide), dilauryl peroxide (dilauryl peroxide), di-tert-butyl peroxide (di-tert-butyl peroxide), tert-butyl peroxy-2-ethyl-hexanoate (t-butyl peroxide-2-ethyl-hexalate), cumene hydroperoxide (cumyl hydroperoxide), and hydrogen peroxide (hydrogen peroxide), or at least one azo group selected from the group consisting of 2,2' -azobis (2-cyanobutane), dimethyl 2,2' -azobis (2-methylpropionate), 2' -azobis (methylbutyronitrile), 2' -azobis (isobutyronitrile) (AIBN; 2,2' -azobis (dimethyl valeronitrile), and 2,2' -azobis (dimethylvaleronitrile) (AMVN; 2,2' -azobis-valrile).
The polymerization initiator may form radicals by thermal dissociation in the battery, and as a non-limiting example, dissociate at a temperature of 30 to 100 ℃ (e.g., 60 to 80 ℃), or dissociate at room temperature (5 to 30 ℃).
The polymerization initiator may be included in an amount of about 10 parts by weight or less, specifically 0.01 parts by weight to 10 parts by weight, and more specifically 5 parts by weight, based on 100 parts by weight of the oligomer. In the case where the amount of the polymerization initiator included is within the above range, since the gelation reaction is easily performed, it is possible to prevent gelation from occurring during the injection of the composition into the battery or to prevent the residual unreacted polymerization initiator from causing side reactions after the polymerization reaction.
In particular, with some polymerization initiators, nitrogen or oxygen may be generated during the generation of radicals by heating. This gas generation most likely causes a gas trap or a gas bubbling phenomenon during the formation of the gel polymer electrolyte. The gas generation causes defects in the gel polymer electrolyte, thus causing deterioration of the electrolyte. Therefore, in the case where the amount of the polymerization initiator included is within the above-described range, adverse factors such as generation of a large amount of gas can be more effectively prevented.
(7) Additive agent
In addition to the effects produced by the ionic liquid, the flame retardant, and the oligomer, the gel polymer electrolyte composition according to the embodiment of the present invention may further include an additional additive that may form a stable film on the surfaces of the negative electrode and the positive electrode without significantly increasing the initial resistance, or may be used as an extender for inhibiting the decomposition of an organic solvent and improving the mobility of lithium ions.
The additional additive is not particularly limited as long as it is an additive for forming a Solid Electrolyte Interface (SEI) that can form a stable film on the surfaces of the positive electrode and the negative electrode.
Specifically, as a representative example, the additive for forming the SEI may include at least one additive for forming the SEI selected from the group consisting of halogen-substituted carbonate-based compounds, nitrile-based compounds, cyclic carbonate-based compounds, phosphate-based compounds, borate-based compounds, and lithium-based compounds.
In particular, the halogen-substituted carbonate-based compound may include fluoroethylene carbonate (FEC), and may be included in an amount of 5 wt% or less based on the total weight of the gel polymer electrolyte composition. In the case where the amount of the halogen-substituted carbonate-based compound is more than 5% by weight, the battery swelling performance may be deteriorated.
Further, the nitrile-based compound may include at least one compound selected from the group consisting of succinonitrile, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanonitrile, cyclopentaonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorobenzonitrile, and 4-fluorobenzonitrile.
In the case where the nitrile-based compound is used together with the above-described mixed additive, effects such as improvement of high-temperature characteristics can be expected due to stabilization of the positive/negative electrode film. That is, the nitrile-based compound may serve as a complementary agent for forming a negative electrode SEI, may play a role in inhibiting solvolysis in an electrolyte, and may play a role in improving mobility of lithium ions. The nitrile compound may be included in an amount of 8 wt% or less based on the total weight of the gel polymer electrolyte composition. In the case where the total amount of the nitrile group compounds in the nonaqueous electrolyte solution is more than 8% by weight, battery performance may be deteriorated due to an increase in resistance caused by an increase in the film formed on the electrode surface.
The carbonate-based compound may improve durability of the battery by forming stable SEI mainly on the surface of the negative electrode during activation of the battery. The cyclic carbonate-based compound may include Vinylene Carbonate (VC) or vinyl ethylene carbonate, and may be included in an amount of 3 wt% or less based on the total weight of the gel polymer electrolyte composition. In the case where the amount of the cyclic carbonate-based compound in the gel polymer electrolyte composition is more than 3% by weight, the battery swelling inhibition performance and initial resistance may be lowered.
In addition, PF in gel polymer electrolyte compositions due to phosphate-based compounds 6 The anions stabilize and contribute to the formation of the positive and negative electrode films, and thus the phosphate-based compound can improve the durability of the battery. The phosphate-based compound may include a compound selected from the group consisting of lithium difluorobis (oxalato) phosphate (LiDFOP), lithium difluorophosphate (LiDFP, liPO) 2 F 2 ) At least one compound of the group consisting of lithium tetrafluoro (oxalate) phosphate (LiTFOP), trimethylsilyl phosphite (TMSPi), tris (2, 2-trifluoroethyl) phosphate (TFEPa), and tris (trifluoroethyl) phosphite (TFEPi), and the phosphate-based compound may be included in an amount of 3 wt% or less based on the total weight of the gel polymer electrolyte composition.
Since the borate-based compound promotes ion pair separation of lithium salt, the borate-based compound may improve mobility of lithium ions, may reduce interface resistance of SEI, and may dissociate materials such as LiF that may be formed during a battery reaction but may not be well separated, and thus, may solve problems such as generation of hydrofluoric acid gas. The borate-based compound may include lithium bis (oxalate) borate (LiBOB) ,LiB(C 2 O 4 ) 2 ) Lithium oxalyldifluoroborate, or lithium tris (trimethylsilyl) borate (TMSB), and the borate-based compound may be included in an amount of 3 wt% or less based on the total weight of the gel polymer electrolyte composition.
In addition, the lithium salt-based compound is a compound different from a lithium salt included in the gel polymer electrolyte composition, wherein the lithium salt-based compound may include a compound selected from the group consisting of LiODFB and LiBF 4 At least one compound of the group constituted, and the lithium-based compound may be included in an amount of 3 wt% or less based on the total weight of the gel polymer electrolyte composition.
Two or more additives for forming the SEI may be mixed and used, and the content of the additives for forming the SEI may be 10 wt% or less, specifically 0.01 wt% to 10 wt%, for example, 0.1 wt% to 5.0 wt%, based on the total weight of the gel polymer electrolyte composition.
In the case where the amount of the additive for forming the SEI is less than 0.01 wt%, the effect of reducing the high temperature storage characteristics and the gas generation by the additive may not be obvious, and in the case where the amount of the additive for forming the SEI is more than 10 wt%, side reactions in the gel polymer electrolyte composition may excessively occur during charge and discharge of the battery. In particular, if an excessive amount of an additive for forming SEI is added, the additive for forming SEI may not be sufficiently dissociated, and thus it may exist in the form of unreacted material or precipitate in the gel polymer electrolyte composition at room temperature. Therefore, the resistance may be increased to deteriorate the life characteristics of the secondary battery.
Gel polymer electrolyte
In addition, in the embodiment of the present invention,
it is possible to provide a gel polymer electrolyte prepared by polymerizing the gel polymer electrolyte composition for a lithium secondary battery of the present invention in an inert atmosphere.
The gel polymer electrolyte of the present invention should have an elastic modulus of at least 100Pa or more so as to be able to maintain a gel form, and in particular, to exhibit excellent performance in a lithium secondary battery, it is desirable to have an elastic modulus of 1,000Pa or more (e.g., 3,000Pa or more).
The modulus of elasticity is measured using a rotary rheometer (DHR 2) in the frequency range of 0.1Hz to 10 Hz.
Specifically, after injecting the gel polymer electrolyte composition into a secondary battery, the gel polymer electrolyte may be prepared by thermal polymerization curing.
For example, the gel polymer electrolyte may be formed by in situ polymerization of the gel polymer electrolyte composition in the secondary battery.
Specifically, the gel polymer electrolyte may be prepared by the steps of:
(a) Inserting an electrode assembly consisting of a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode into a battery case;
(b) Injecting the gel polymer electrolyte composition according to the present invention into a battery case;
(c) Wetting and aging the electrode assembly; and
(d) The gel polymer electrolyte composition is polymerized to form a gel polymer electrolyte.
In this case, the in-situ polymerization reaction in the lithium secondary battery may be performed by using an electron beam (E-beam), gamma rays, and a room temperature or high temperature aging process, and, according to an embodiment of the present invention, the in-situ polymerization reaction may be performed by thermal polymerization. In this case, the desired polymerization time may be in the range of about 2 minutes to about 48 hours, and the thermal polymerization temperature may be in the range of 60 ℃ to 100 ℃ (e.g., 60 ℃ to 80 ℃).
Specifically, in an in-situ polymerization reaction in a lithium secondary battery, a polymerization initiator, an oligomer, an ionic liquid, and a flame retardant are added to a nonaqueous organic solvent in which a lithium salt is dissolved, and mixed, and then the mixture is injected into a battery cell. After sealing the electrolyte injection hole of the battery cell, the gel polymer electrolyte of the present invention may be prepared by heating the battery cell to about 60 to about 80 ℃ for 1 to 20 hours by performing thermal polymerization.
Lithium secondary battery
In addition, in the embodiment of the present invention,
there is provided a lithium secondary battery comprising a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and the gel polymer electrolyte of the present invention prepared by the above method.
The lithium secondary battery according to the embodiment of the present invention has a charging voltage range of 3.0V to 5.0V, and thus, the capacity characteristics of the lithium secondary battery may be excellent in both a normal voltage and a high voltage range.
In addition, since the quality deterioration phenomenon occurring during storage and transportation of the electrolyte is reduced, the overall cost can be reduced and the long-term storage stability at high temperature and high voltage can be further improved.
In particular, in the lithium secondary battery of the present invention, the electrode assembly may be formed by sequentially stacking the positive electrode, the negative electrode, and the separator disposed between the positive electrode and the negative electrode. In this case, those positive electrodes, negative electrodes and separators prepared by a typical method and used for preparing a lithium secondary battery may be used as the positive electrodes, negative electrodes and separators constituting the electrode assembly.
(1) Positive electrode
First, a positive electrode may be prepared by forming a positive electrode material mixture layer on a positive electrode current collector. The positive electrode material mixture layer may be prepared by coating a positive electrode current collector with a positive electrode slurry including a positive electrode active material, a binder, a conductive agent, and a solvent, and then drying and rolling the coated positive electrode current collector.
The positive electrode current collector is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery, and, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, or the like may be used.
The positive electrode active material is a compound capable of reversibly intercalating and deintercalating lithium, wherein the positive electrode active material may specifically include a transition metal oxide represented by formula 9, wherein the amount of nickel (Ni) is 0.8 or more.
[ 9]
Li(Ni a1 Co b1 Mn c1 )O 2
(in the formula 9 of the present invention,
a1<0.9,0.05< b1<0.17,0.05< c1<0.17, and a1+b1+c1=1. )
Specifically, the positive electrode active material is a transition metal oxide having a high Ni content, wherein the positive electrode active material may include Li (Ni 0.8 Mn 0.1 Co 0.1 )O 2 。
Since the structural stability of the transition metal oxide having a high Ni content as described above is insufficient due to heating, the transition metal oxide having a high Ni content has a disadvantage in that the positive electrode is deteriorated during heat curing for preparing the gel polymer electrolyte. In addition, since the gel polymer electrolyte has insufficient oxidation stability, HF (one of side reaction products of the electrolyte) attacks the positive electrode active material having a high Ni content during the operation of the battery to reduce the positive electrode component.
Therefore, since the gel polymer electrolyte including the ionic liquid having a low transition metal dissociation degree is used in the present invention, dissolution of the transition metal in the positive electrode active material can be suppressed. In addition, since side reactions at the interface between the electrode and the electrolyte can be prevented by using the gel polymer electrolyte having excellent oxidation stability, a secondary battery having improved high-temperature storage characteristics can be manufactured.
The positive electrode active material may further include a lithium manganese-based oxide (e.g., liMnO 2 、LiMn 2 O 4 Etc.), lithium cobalt-based oxides (e.g., liCoO 2 Etc.), lithium nickel-based oxides (e.g., liNiO 2 Etc.); lithium nickel manganese-based oxide (e.g., liNi 1-Y Mn Y O 2 (wherein 0<Y<1)、LiMn 2-Z Ni Z O 4 (wherein 0<Z<2) Etc.), lithium nickel cobalt-based oxide (e.g., liNi 1-Y1 Co Y1 O 2 (wherein 0<Y1<1) Lithium manganese cobalt-based oxide (e.g., liCo) 1-Y2 Mn Y2 O 2 (wherein 0<Y2<1)、LiMn 2-Z1 Co Z1 O 4 (wherein 0<Z1<2) Etc.), or lithium nickel cobalt transition metal (M) oxide (e.g., li (Ni) p2 Co q2 Mn r3 M S2 )O 2 (wherein M is selected from the group consisting of aluminum (Al), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), tantalum (Ta), magnesium (Mg), and molybdenum (Mo), and p2, q2, r3, and s2 are the atomic fractions of each individual element, wherein 0 <p2<1,0<q2<1,0<r3<1,0<S2<1, and p3+q3+r3+s1=1), etc.), and may include any one of them or a mixture of two or more of them.
Among these materials, the lithium composite metal oxide may include LiCoO in terms of improving capacity characteristics and stability of the battery 2 、LiMnO 2 、LiNiO 2 Lithium nickel manganese cobalt oxide (e.g., li (Ni 1/3 Mn 1/3 Co 1/3 )O 2 、Li(Ni 0.6 Mn 0.2 Co 0.2 )O 2 、Li(Ni 0.7 Mn 0.15 Co 0.15 )O 2 And Li (Ni) 0.5 Mn 0.3 Co 0.2 )O 2 ) Or lithium nickel cobalt aluminum oxide (e.g., liNi 0.8 Co 0.15 Al 0.05 O 2 Etc.).
The positive electrode active material may be included in an amount of 80 to 99 wt%, for example, 85 to 95 wt%, based on the total weight of solids in the positive electrode slurry. In the case where the amount of the positive electrode active material is 80 wt% or less, the capacity may be reduced due to a decrease in energy density.
The binder is a component that contributes to the bonding between the active material and the conductive agent and to the bonding with the current collector, wherein the binder is generally added in an amount of 1 to 30% by weight based on the total weight of solids in the positive electrode slurry. Examples of binders may be polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymers (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, and the like.
Any conductive agent may be used as the conductive agent without particular limitation as long as it has conductivity and does not cause adverse chemical changes in the battery, and for example, conductive materials such as the following may be used: carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder, such as natural graphite, artificial graphite, or graphite having a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or a polyphenylene derivative.
The conductive agent is generally added in an amount of 1 to 30% by weight based on the total weight of solids in the positive electrode slurry.
The solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount such that a desired viscosity is obtained when a positive electrode active material and optionally a binder and a conductive agent are included. For example, the solvent may be included in an amount such that the concentration of solids in the slurry including the positive electrode active material and optionally including the binder and the conductive agent is in the range of 10 to 70 wt% (e.g., 20 to 60 wt%).
(2) Negative electrode
The anode may be prepared by forming an anode material mixture layer on an anode current collector. The anode material mixed layer may be prepared by coating an anode current collector with an anode slurry including an anode active material, a binder, a conductive agent, and a solvent, and then drying and rolling the coated anode current collector.
The negative electrode current collector generally has a thickness of 3 μm to 500 μm. The anode current collector is not particularly limited as long as it has high conductivity and does not cause adverse chemical changes in the battery, and, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like may be used. Further, the anode current collector may have fine surface roughness to improve the adhesive strength with the anode active material, similarly to the cathode current collector, and the anode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric body, and the like.
Further, the anode active material may include at least one selected from the group consisting of: lithium metal, carbon materials capable of reversibly intercalating/deintercalating lithium ions, metals or alloys of lithium with these metals, metal composite oxides, materials that can be doped and undoped with lithium, and transition metal oxides.
As the carbon material capable of reversibly intercalating/deintercalating lithium ions, a carbon-based anode active material commonly used in lithium ion secondary batteries may be used without particular limitation, and as a typical example, crystalline carbon, amorphous carbon, or both thereof may be used. Examples of crystalline carbon may be graphite such as irregular, planar, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of amorphous carbon may be soft carbon (low temperature sintered carbon) or hard carbon (hard carbon), mesophase pitch carbide, and fired coke.
As the metal or the alloy of lithium and the metal, a metal selected from the group consisting of: copper (Cu), nickel (Ni), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), silicon (Si), antimony (Sb), lead (Pb), indium (In), zinc (Zn), barium (Ba), radium (Ra), germanium (Ge), aluminum (Al), and tin (Sn), or alloys of lithium and the metal.
As the metal composite oxide, one selected from the group consisting of: pbO, pbO 2 、Pb 2 O 3 、Pb 3 O 4 、Sb 2 O 3 、Sb 2 O 4 、Sb 2 O 5 、GeO、GeO 2 、Bi 2 O 3 、Bi 2 O 4 、Bi 2 O 5 、Li x5 Fe 2 O 3 (0≤x5≤1)、Li x6 WO 2 (0.ltoreq.x6.ltoreq.1), and Sn x7 Me 1-x7 Me' y O z (Me: manganese (Mn), fe, pb, or Ge; me': al, boron (B), phosphorus (P), si, an element of groups I, II, III of the periodic Table, or halogen; 0) <x7≤1；1≤y≤3；1≤z≤8)。
The materials that can be doped and undoped lithium can include Si, siO x8 (0<x 8.ltoreq.2), si-Y alloy (wherein Y is an element selected from the group consisting of: alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, and combinations thereof, and Y is not Si), sn, snO 2 And Sn-Y (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, and Y is not Sn), and SiO may also be used 2 And at least one of them. Element Y may be selected from the group consisting of: mg, ca, sr, ba, ra, scandium (Sc), yttrium (Y), ti, zirconium (Zr), hafnium (Hf), (Rf), V, niobium (Nb), ta, (Db), cr, mo, tungsten (W), (Sg), technetium (Tc), rhenium (Re), (Bh), fe, pb, ruthenium (Ru), osmium (Os), (Hs), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), cu, silver (Ag), gold (Au), zn, cadmium (Cd), B, al, gallium (Ga), sn, in, ge, P, arsenic (As), sb, bismuth (Bi), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and combinations thereof.
The transition metal oxide may include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.
The anode active material may be included in an amount of 80 to 99 wt% based on the total weight of solids in the anode slurry.
The binder is a component that contributes to the bonding between the conductive agent, the active material, and the current collector, wherein the binder is generally added in an amount of 1 to 30% by weight based on the total weight of solids in the anode slurry. Examples of binders may be polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymers (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.
The conductive agent is a component for further improving the conductivity of the anode active material, wherein the conductive agent may be added in an amount of 1 to 20 wt% based on the total weight of solids in the anode slurry. Any conductive agent may be used without particular limitation as long as it has conductivity and does not cause adverse chemical changes in the battery, and for example, conductive materials such as the following may be used: carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder, such as natural graphite, artificial graphite, or graphite having a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or a polyphenylene derivative.
The solvent may include water or an organic solvent such as NMP and alcohol, and may be used in an amount such that a desired viscosity is obtained when the anode active material and optionally the binder and the conductive agent are included. For example, the solvent may be included in an amount such that the concentration of solids in the slurry including the anode active material and optionally including the binder and the conductive agent is in the range of 50 to 75 wt% (e.g., 50 to 65 wt%).
(3) Partition board
In addition, the separator serves to prevent an internal short circuit between two electrodes and impregnate an electrolyte, wherein the separator composition is directly coated on the electrodes and dried to form a separator after the polymer resin, the filler and the solvent are mixed to prepare the separator composition, or the separator may be prepared by laminating the separator peeled from the support on the electrodes after the separator composition is cast on the support and dried.
A porous polymer film generally used, for example, a porous polymer film made from a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, may be used alone as a separator or a laminate formed from them as a separator. In addition, a typical porous nonwoven fabric, for example, a nonwoven fabric formed of high-melting glass fibers or polyethylene terephthalate fibers may be used, but the present invention is not limited thereto.
In this case, the porous separator may generally have a pore size of 0.01 μm to 50 μm and a porosity of 5% to 95%. In addition, the porous separator may generally have a thickness of 5 μm to 300 μm.
The shape of the lithium secondary battery of the present invention is not particularly limited, but a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape (coin) may be used.
Hereinafter, the present invention will be described in more detail according to examples. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Furthermore, these exemplary embodiments are provided so that this description will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
Examples
Example 1.
(preparation of gel Polymer electrolyte composition for lithium Secondary Battery)
Gel polymer electrolyte compositions (see table 1 below) were prepared by adding 20g of ethylmethylimidazolium-bis (fluorosulfonyl) imide (EMI-FIS) as an ionic liquid, 5g of an oligomer represented by formula 1a (weight average molecular weight (Mw): 3,000, n1=5, m1=5, x1=10), 10g of a compound represented by formula 8a as a flame retardant, and 0.01g of dimethyl 2,2' -azobis (2-methylpropionate) (CAS No. 2589-57-3) as a polymerization initiator to 64.99g of a nonaqueous organic solvent in which 1.0M LiFSI is dissolved (ethylene carbonate (EC): methyl ethyl carbonate (EMC) =3:7 in volume ratio.
(electrode Assembly preparation)
Li (Ni) 0.8 Mn 0.1 Co 0.1 )O 2 Carbon black (carbon black), and polyvinylidene fluoride (PVDF) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 94:3:3 to prepare a positive electrode mixed slurry. An aluminum (Al) film of about 20 μm thickness as a positive electrode current collector was coated with the positive electrode mixed slurry and dried, and then the coated Al film was roll pressed to prepare a positive electrode.
Graphite, PVDF, and carbon black (carbon black) as anode active materials were added to NMP as a solvent in a weight ratio of 96:3:1 to prepare an anode mixed slurry. A 10 μm thick copper (Cu) thin film as a negative electrode current collector was coated with the negative electrode mixed slurry and dried, and then the coated Cu thin film was rolled (roll press) to prepare a negative electrode.
An electrode assembly was prepared by sequentially stacking the positive electrode, a separator formed of three layers of polypropylene/polyethylene/polypropylene (PP/PE/PP), and the negative electrode.
(preparation of secondary cell)
The assembled electrode assembly was put into a battery case, and the gel polymer electrolyte composition for a lithium secondary battery prepared as described above was injected thereinto, thermal polymerization was performed at 60 ℃ for 24 hours, and then the battery case was stored at room temperature for 2 days to prepare a lithium secondary battery including the gel polymer electrolyte for a lithium secondary battery.
Example 2.
A gel polymer electrolyte composition for a lithium secondary battery and a lithium secondary battery including the gel polymer electrolyte prepared therefrom were prepared in the same manner as in example 1, except that: during the preparation of the gel polymer electrolyte composition for lithium secondary batteries, methylpropylpyrrolidinium-bis (fluorosulfonyl) imide (Pyr 13-FSI) was used as an ionic liquid instead of ethylmethylimidazolium-bis (fluorosulfonyl) imide (EMI-FIS) (see table 1 below).
Example 3.
A gel polymer electrolyte composition for a lithium secondary battery and a lithium secondary battery including the gel polymer electrolyte prepared therefrom were prepared in the same manner as in example 1, except that: during the preparation of the gel polymer electrolyte composition for a lithium secondary battery, an oligomer represented by formula 2a (weight average molecular weight (Mw): 5,000, p1=5, q1=10) was used instead of the oligomer represented by formula 1a as an oligomer (see table 1 below).
Example 4.
A gel polymer electrolyte composition for a lithium secondary battery and a lithium secondary battery including the gel polymer electrolyte prepared therefrom were prepared in the same manner as in example 2, except that: during the preparation of the gel polymer electrolyte composition for a lithium secondary battery, an oligomer represented by formula 2a (weight average molecular weight (Mw): 5,000, p1=5, q1=10) was used instead of the oligomer represented by formula 1a as an oligomer (see table 1 below).
Example 5.
(preparation of gel Polymer electrolyte composition for lithium Secondary Battery)
Gel polymer electrolyte compositions (see table 1 below) were prepared by adding 50g of ethylmethylimidazolium-bis (fluorosulfonyl) imide (EMI-FIS) as an ionic liquid, 5g of an oligomer represented by formula 1a (weight average molecular weight (Mw): 3,000, n1=5, m1=5, x1=10), 10g of a compound represented by formula 8a as a flame retardant, and 0.01g of dimethyl 2,2' -azobis (2-methylpropionate) (CAS number: 2589-57-3) as a polymerization initiator to 34.99g of a nonaqueous organic solvent in which 1.0M LiFSI is dissolved (EC: 3:7 in a volume ratio).
(preparation of secondary cell)
A lithium secondary battery including a gel polymer electrolyte was prepared in the same manner as in example 1, except that: the gel polymer electrolyte composition prepared as described above was used.
Example 6.
(preparation of gel Polymer electrolyte composition for lithium Secondary Battery)
Gel polymer electrolyte compositions (see table 1 below) were prepared by adding 5g of ethylmethylimidazolium-bis (fluorosulfonyl) imide (EMI-FIS) as an ionic liquid, 30g of an oligomer represented by formula 1a (weight average molecular weight (Mw): 3,000, n1=5, m1=5, x1=10), 10g of a compound represented by formula 8a as a flame retardant, and 0.01g of dimethyl 2,2' -azobis (2-methylpropionate) (CAS number: 2589-57-3) as a polymerization initiator to 54.99g of a nonaqueous organic solvent in which 1.0M LiFSI is dissolved (EC: 3:7 in a volume ratio).
(preparation of secondary cell)
A lithium secondary battery including a gel polymer electrolyte was prepared in the same manner as in example 1, except that: the gel polymer electrolyte composition prepared as described above was used.
Example 7.
(preparation of gel Polymer electrolyte composition for lithium Secondary Battery)
Gel polymer electrolyte compositions (see table 1 below) were prepared by adding 10g of ethylmethylimidazolium-bis (fluorosulfonyl) imide (EMI-FIS) as an ionic liquid, 5g of an oligomer represented by formula 1a (weight average molecular weight (Mw): 3,000, n1=5, m1=5, x1=10), 30g of a compound represented by formula 8a as a flame retardant, and 0.01g of dimethyl 2,2' -azobis (2-methylpropionate) (CAS number: 2589-57-3) as a polymerization initiator to 54.99g of a nonaqueous organic solvent in which 1.0M LiFSI is dissolved (EC: 3:7 in a volume ratio).
(preparation of secondary cell)
A lithium secondary battery including a gel polymer electrolyte was prepared in the same manner as in example 1, except that: the gel polymer electrolyte composition prepared as described above was used.
Example 8.
(preparation of gel Polymer electrolyte composition for lithium Secondary Battery)
Gel polymer electrolyte compositions were prepared by adding 1g of ethylmethylimidazolium-bis (fluorosulfonyl) imide (EMI-FIS) as an ionic liquid, 0.5g of an oligomer represented by formula 1a (weight average molecular weight (Mw): 3,000, n1=5, m1=5, x1=10), 1g of a compound represented by formula 8a as a flame retardant, and 0.01g of dimethyl 2,2' -azobis (2-methylpropionate) (CAS number: 2589-57-3) as a polymerization initiator to 97.49g of a nonaqueous organic solvent in which 1.0M LiFSI is dissolved (EC: emc=3:7 in a volume ratio) (see table 1 below).
(preparation of secondary cell)
A lithium secondary battery including a gel polymer electrolyte was prepared in the same manner as in example 1, except that: the gel polymer electrolyte composition prepared as described above was used.
Example 9.
(preparation of gel Polymer electrolyte composition for lithium Secondary Battery)
Gel polymer electrolyte compositions (see table 1 below) were prepared by adding 30g of ethylmethylimidazolium-bis (fluorosulfonyl) imide (EMI-FIS) as an ionic liquid, 20g of an oligomer represented by formula 1a (weight average molecular weight (Mw): 3,000, n1=5, m1=5, x1=10), 10g of a compound represented by formula 8a as a flame retardant, and 0.01g of dimethyl 2,2' -azobis (2-methylpropionate) (CAS number: 2589-57-3) as a polymerization initiator to 39.99g of a nonaqueous organic solvent in which 1.0M LiFSI is dissolved (EC: 3:7 in a volume ratio).
(preparation of secondary cell)
A lithium secondary battery including a gel polymer electrolyte was prepared in the same manner as in example 1, except that: the gel polymer electrolyte composition prepared as described above was used.
Comparative example 1.
(preparation of gel Polymer electrolyte composition)
A gel polymer electrolyte composition was prepared by adding 5g of an oligomer (weight average molecular weight (Mw): 3,000, n1=5, m1=5, x1=10) represented by formula 1a, and 0.01g of dimethyl 2,2' -azobis (2-methylpropionate) as a polymerization initiator to 94.99g of a nonaqueous organic solvent (EC: emc=3:7 in volume ratio) in which 1.0M LiFSI was dissolved.
(preparation of secondary cell)
A lithium secondary battery including a gel polymer electrolyte was prepared in the same manner as in example 1, except that: the gel polymer electrolyte composition prepared as described above was used.
Comparative example 2.
(preparation of gel Polymer electrolyte composition)
Gel polymer electrolyte compositions were prepared by adding 20g of ethylmethylimidazolium-bis (fluorosulfonyl) imide (EMI-FIS) as an ionic liquid, 5g of an oligomer represented by formula 1a (weight average molecular weight (Mw): 3,000, n1=5, m1=5, x1=10), and 0.01g of dimethyl 2,2' -azobis (2-methylpropionate) as a polymerization initiator to 74.99g of a nonaqueous organic solvent in which 1.0M LiFSI is dissolved (EC: emc=3:7 in volume ratio) (see table 1 below).
(preparation of secondary cell)
A lithium secondary battery including a gel polymer electrolyte was prepared in the same manner as in example 1, except that: the gel polymer electrolyte composition prepared as described above was used.
Comparative example 3.
A gel polymer electrolyte composition for a lithium secondary battery and a lithium secondary battery including the gel polymer electrolyte prepared therefrom were prepared in the same manner as in example 2, except that: during the preparation of the gel polymer electrolyte composition for lithium secondary batteries, methylpropylpyrrolidinium-bis (fluorosulfonyl) imide (Pyr 13-FSI) was used as an ionic liquid instead of ethylmethylimidazolium-bis (fluorosulfonyl) imide (EMI-FIS) (see table 1 below).
Comparative example 4.
(preparation of gel Polymer electrolyte composition)
Gel polymer electrolyte compositions were prepared by adding 5g of an oligomer (weight average molecular weight (Mw): 3,000, n1=5, m1=5, x1=10) represented by formula 1a, 10g of a compound represented by formula 8a as a flame retardant, and 0.01g of dimethyl 2,2' -azobis (2-methylpropionate) as a polymerization initiator to 84.99g of a nonaqueous organic solvent (EC: emc=3:7 in a volume ratio) in which 1.0M LiFSI was dissolved (see table 1 below).
(preparation of secondary cell)
A lithium secondary battery including a gel polymer electrolyte was prepared in the same manner as in example 1, except that: the gel polymer electrolyte composition prepared as described above was used.
TABLE 1
In Table 1, EMI-FIS represents ethylmethylimidazolium-bis (fluorosulfonyl) imide and Pyr13-FSI represents methylpropylpyrrolidinium-bis (fluorosulfonyl) imide.
Test examples
Test example 1: flame retardant (spontaneous combustion) test
A self-extinguishment time (self-extinguishtime) test was performed in which 1g of each of the gel polymer electrolyte compositions for lithium secondary batteries prepared in examples 1 to 9 and 1g of each of the gel polymer electrolyte compositions for lithium secondary batteries prepared in comparative examples 1 to 4 were respectively ignited to measure the time before ignition of each sample to evaluate flame retardancy. The results are shown in Table 2 below.
TABLE 2
| SET (second) | |
| Example 1 | 0 |
| Example 2 | 0 |
| Example 3 | 0 |
| Example 4 | 0 |
| Example 5 | 0 |
| Example 6 | 0 |
| Example 7 | 0 |
| Example 8 | 0 |
| Example 9 | 0 |
| Comparative example 1 | 10 |
| Comparative example 2 | 5 |
| Comparative example 3 | 5 |
| Comparative example 4 | 5 |
Referring to table 2, it can be understood that the gel polymer electrolyte compositions for lithium secondary batteries prepared in examples 1 to 9 were not ignited, but the gel polymer electrolyte compositions of comparative example 1, which did not include the ionic liquid and the flame retardant but included only the carbonate-based solvent, the gel polymer electrolyte compositions of comparative examples 2 and 3, which did not include the flame retardant, and the gel polymer electrolyte compositions of comparative example 4, which did not include the ionic liquid, were not only ignited, but also the ignition time (SET value) was within 10 seconds or less.
From these results, it can be understood that the gel polymer electrolyte compositions for lithium secondary batteries of examples 1 to 9 were improved in flame retardancy as compared with the gel polymer electrolyte compositions of comparative examples 1 to 4.
Test example 2: thermal value test
The lithium secondary batteries prepared in examples 1 to 9 and comparative examples 1 to 4 were fully charged to 4.2V, respectively, and then disassembled to separate the positive electrodes. After the positive electrode active material layer was scraped off from the positive electrode obtained from each lithium secondary battery to obtain a powder, the powder was charged into a differential scanning calorimeter (Differential Scanning Calorimeter (DSC), DSC-01,METTLER TOLEDO) and an exothermic start point (onset point) and a Heat Flow (Heat Flow) were measured while heating from 25 ℃ to 400 ℃ at a heating rate of 10 ℃/min. DSC measurements were repeated three or more times to calculate an average. The results are shown in Table 3 below.
TABLE 3
| Sample of | Exothermic onset (. Degree. C.) of heat | Heat flow (J/g) |
| Example 1 | 280 | 10< |
| Example 2 | 280 | 10< |
| Example 3 | 280 | 10< |
| Example 4 | 280 | 10< |
| Example 5 | 280 | 10< |
| Example 6 | 280 | 10< |
| Example 7 | 280 | 10< |
| Example 8 | 280 | 10< |
| Example 9 | 280 | 10< |
| Comparative example 1 | 250 | 97.5 |
| Comparative example 2 | 270 | 70.2 |
| Comparative example 3 | 270 | 65.4 |
| Comparative example 4 | 262 | 75.0 |
In general, the structure of a positive electrode in a fully charged state is in a lithium deintercalated state, in which oxygen radicals are generated while the structure of the positive electrode collapses when the positive electrode is left standing at a high temperature because the positive electrode is structurally unstable. The electrodes are placed at an elevated temperature. Since the oxygen radicals generated in this case have very high reactivity, the oxygen radicals cause exothermic reactions while reacting with the electrolyte.
Referring to table 3, regarding the lithium secondary batteries including the gel polymer electrolyte including the flame retardant and the ionic liquid having relatively low reactivity with oxygen radicals prepared in examples 1 to 9, it is understood that the exothermic reaction of the obtained positive electrode active material starts from 280 ℃ and the heat flow is low to about 10J/g or less.
In contrast, regarding the lithium secondary battery of comparative example 1 including the gel polymer electrolyte containing no both the ionic liquid and the flame retardant, it is understood that the exothermic reaction starts from a relatively low temperature of 250 c and the heat flow is as high as 97.5J/g due to structural collapse of the positive electrode and the reaction of oxygen radicals generated in this case with the electrolyte.
Further, regarding the lithium secondary batteries of comparative examples 2 and 3 including the gel polymer electrolyte without flame retardant, it is understood that the heat flow was higher than the secondary batteries of examples 1 to 9 because the heat release starting point was raised to 270 ℃ due to the inclusion of the ionic liquid, but the effect was not obvious.
Regarding the lithium secondary battery of comparative example 4 including the gel polymer electrolyte containing no ionic liquid, it is understood that not only the exothermic reaction starts from a relatively low temperature of 262 c but also the heat flow is as high as 75.0J/g.
From these results, it was confirmed that the high temperature stability of the lithium secondary batteries of examples 1 to 9 of the present invention was superior to that of the secondary batteries of comparative examples 1 to 4.
Test example 3: hot box test
A hot box test was performed in which the lithium secondary batteries prepared in examples 1 to 9 and the lithium secondary batteries prepared in comparative examples 1 to 4 were heated to 150 ℃ in a fully charged state (i.e., state of charge (SOC) of 100%) at a heating rate of 5 ℃/min, and then were respectively left to stand for 30 minutes to confirm whether fire was present. The results are shown in Table 4 below.
TABLE 4
In table 4, x represents a case where no ignition occurred during storage at 150 ℃, and O represents a case where ignition occurred during storage at 150 ℃.
Referring to table 4, regarding the lithium secondary batteries prepared in examples 1 to 9, since stability was improved even during storage at a high temperature of 150 ℃ in a fully charged state by the gel polymer electrolyte including the ionic liquid and the flame retardant, exothermic reaction was reduced, and thus, it can be understood that ignition did not occur.
In contrast, regarding the lithium secondary battery of comparative example 1 including the gel polymer electrolyte containing no both the ionic liquid and the flame retardant, it is understood that the secondary battery was ignited after 10 minutes after the temperature was raised to 150 ℃ due to the occurrence of the thermal runaway phenomenon.
Regarding the secondary batteries of comparative examples 2 and 3 including the gel polymer electrolyte containing the ionic liquid, it is understood that the batteries catch fire after 20 minutes after the temperature is raised to 150 ℃. That is, with respect to the secondary batteries of comparative examples 2 and 3, it is understood that the ignition start time is increased as compared to comparative example 1 due to the inclusion of the ionic liquid, but the ignition is not completely suppressed eventually.
Further, regarding the secondary battery of comparative example 4 including the gel polymer electrolyte containing only the flame retardant, it is understood that the battery was ignited after 20 minutes after the temperature was increased to 150 ℃. That is, with respect to the secondary battery of comparative example 4, it is understood that the ignition start time is increased as compared to comparative example 1 due to inclusion of the flame retardant, but the ignition is not completely suppressed in the end.
Claims (15)
1. A gel polymer electrolyte composition for a lithium secondary battery, the gel polymer electrolyte composition comprising:
lithium salt, nonaqueous organic solvent, ionic liquid, oligomer, flame retardant and polymerization initiator,
wherein the oligomer includes at least one selected from the group consisting of oligomers represented by formulas 1 and 2:
[ 1]
Wherein, in the formula 1,
r is an aliphatic hydrocarbon group or an aromatic hydrocarbon group,
R a 、R b 、R c and R d Each independently is a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms,
R e is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms,
r 'and R' are each independently hydrogen, or alkyl having 1 to 3 carbon atoms,
a is an integer of one of 1 to 3,
b is an integer of one of 0 to 2,
n, m and x are the number of repeating units,
n is an integer of one of 1 to 10,
m is an integer of one of 1 to 5, and
x is an integer of one of 1 to 15,
[ 2]
Wherein, in the formula 2,
R f an alkylene radical having 1 to 5 carbon atoms which is unsubstituted or substituted by at least one fluorine,
R g 、R h 、R i and R j Each independently is a fluorine element, or a fluorine substituted or unsubstituted alkyl group having 1 to 3 carbon atoms,
R 0 Is an aliphatic hydrocarbon group or an aromatic hydrocarbon group,
r' "is hydrogen, or an alkyl group having 1 to 3 carbon atoms,
o is an integer of one of 1 to 3,
p and q are the number of repeating units,
p is an integer of one of 1 to 10, and
q is an integer of one of 1 to 15,
wherein the ionic liquid comprises a compound selected from the group consisting of BF 4 - 、PF 6 - 、ClO 4 - Bis (fluorosulfonyl) imide (N (SO) 2 F) 2 - ) (bis) trifluoromethanesulfonyl imide (N (SO) 2 CF 3 ) 2 - ) Bis-perfluoroethanesulfonylimide (N (SO) 2 C 2 F 5 ) 2 - ) And oxalyl difluoroborate (BF 2 (C 2 O 4 ) - ) At least one of the groups being formed as an anionic component, and
comprising, as a cationic component, at least one selected from the group consisting of cations represented by formulas 3 to 7:
[ 3]
Wherein, in the formula 3,
R 1 、R 2 、R 3 and R is 4 Each independently hydrogen, or an alkyl group having 1 to 5 carbon atoms,
[ 4]
Wherein, in the formula 4,
R 5 and R is 6 Each independently is an alkyl group having 1 to 5 carbon atoms,
[ 5]
Wherein, in the formula 5,
R 7 and R is 8 Each independently is an alkyl group having 1 to 5 carbon atoms,
[ 6]
Wherein, in the formula 6,
R 9 、R 10 、R 11 and R 12 Each independently is an alkyl group having 1 to 5 carbon atoms, [ formula 7 ]]
Wherein, in the formula 7,
R 13 、R 14 、R 15 and (d) sumR 16 Each independently is an alkyl group having 1 to 5 carbon atoms,
Wherein the flame retardant is a compound represented by formula 8:
[ 8]
Wherein, in the formula 8,
R 17 、R 18 、R 19 、R 20 、R 21 and R 22 Each independently is selected from the group consisting of H, F, -CF 3 、-CF 2 CF 3 、-C(CF 3 ) 3 、-Cl、-CCl 3 、-CF 2 CCl 3 、-C(CCl 3 ) 3 、-Br、-CBr 3 、-CBr 2 CBr 3 、-C(CBr 3 ) 3 、I、-CI 3 、-CI 2 CI 3 and-C (CI) 3 ) 3 One of the groups formed, and
R 17 、R 18 、R 19 、R 20 、R 21 and R 22 Comprises at least one selected from the group consisting of F, cl, br and I.
2. The gel polymer electrolyte composition for a lithium secondary battery according to claim 1, wherein the cation represented by formula 3 is selected from the group consisting of cations represented by formulas 3a and 3 b:
[ 3a ]
[ 3b ]
3. The gel polymer electrolyte composition for a lithium secondary battery according to claim 1, wherein the cation represented by formula 4 is selected from the group consisting of cations represented by formulas 4a and 4 b:
[ 4a ]
[ 4b ]
4. The gel polymer electrolyte composition for a lithium secondary battery according to claim 1, wherein the cation represented by formula 5 is selected from the group consisting of cations represented by formulas 5a and 5 b:
[ 5a ]
[ 5b ]
5. The gel polymer electrolyte composition for a lithium secondary battery according to claim 1, wherein the cation represented by formula 7 is a cation represented by formula 7 a:
[ 7a ]
6. The gel polymer electrolyte composition for a lithium secondary battery according to claim 1, wherein the ionic liquid is included in an amount of 1 to 50 wt% based on the total weight of the gel polymer electrolyte composition for a lithium secondary battery.
7. The gel polymer electrolyte composition for a lithium secondary battery according to claim 1, wherein in formula 1 or formula 2, R or R 0 Comprises at least one member selected from the group consisting of (a) at least one alicyclic hydrocarbon group and (b) at least one straight chain hydrocarbon group, wherein (a) alicyclic hydrocarbon group is selected from the group consisting of: a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms, a substituted or unsubstituted cycloalkenylene group having 4 to 20 carbon atoms, and a substituted or unsubstituted heterocycloalkylene group having 2 to 20 carbon atoms, and (b) a linear hydrocarbon group is selected from the group consisting of: a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms, a substituted or unsubstituted alkylene group having 2 to 20 carbon atoms, and a substituted or unsubstituted alkynylene group having 2 to 20 carbon atoms, and
r or R 0 Comprises at least one selected from the group consisting of a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, and a substituted or unsubstituted heteroarylene group having 2 to 20 carbon atoms.
8. The gel polymer electrolyte composition for a lithium secondary battery according to claim 1, wherein the oligomer represented by formula 1 is an oligomer represented by formula 1 a:
[ 1a ]
Wherein, in the formula 1a,
n1, m1 and x1 are the number of repeating units,
n1 is an integer of one of 1 to 10,
m1 is an integer of one of 1 to 5, and
x1 is an integer from 1 to 15.
9. The gel polymer electrolyte composition for a lithium secondary battery according to claim 1, wherein the oligomer represented by formula 2 is an oligomer represented by formula 2 a:
[ 2a ]
Wherein, in the formula 2a,
p1 and q1 are the number of repeating units,
p1 is an integer of one of 1 to 10, and
q1 is an integer of one of 1 to 15.
10. The gel polymer electrolyte composition for a lithium secondary battery according to claim 1, wherein the oligomer is included in an amount of 0.1 to 30 wt% based on the total weight of the gel polymer electrolyte composition for a lithium secondary battery.
11. The gel polymer electrolyte composition for a lithium secondary battery according to claim 1, wherein the compound represented by formula 8 includes at least one selected from the group consisting of compounds represented by formulas 8a to 8 d:
[ 8a ]
[ 8b ]
[ 8c ]
[ 8d ]
12. The gel polymer electrolyte composition for a lithium secondary battery according to claim 1, wherein the flame retardant is included in an amount of 1 to 30 wt% based on the total weight of the gel polymer electrolyte composition for a lithium secondary battery.
13. A gel polymer electrolyte prepared by polymerizing the gel polymer electrolyte composition for a lithium secondary battery according to claim 1.
14. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and the gel polymer electrolyte of claim 13.
15. The lithium secondary battery according to claim 14, wherein the positive electrode includes a positive electrode active material represented by formula 9:
[ 9]
Li(Ni a1 Co b1 Mn c1 )O 2
Wherein, in the formula 9,
a1<0.9,0.05< b1<0.17,0.05< c1<0.17, and a1+b1+c1=1.
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| JP2013254633A (en) * | 2012-06-06 | 2013-12-19 | Asahi Kasei Corp | Electrolyte for electrochemical device, and lithium ion secondary battery |
| CN104981934A (en) * | 2012-11-12 | 2015-10-14 | 诺莱特科技公司 | Non-aqueous electrolytic solutions and electrochemical cells comprising same |
| CN106797048A (en) * | 2014-10-02 | 2017-05-31 | 株式会社Lg化学 | Gel polymer electrolyte and the lithium secondary battery including the gel polymer electrolyte |
| WO2017179468A1 (en) * | 2016-04-12 | 2017-10-19 | ダイキン工業株式会社 | Electrolyte solution, electrochemical device, lithium ion secondary battery and module |
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| CA2625271A1 (en) | 2008-03-11 | 2009-09-11 | Hydro-Quebec | Method for preparing an electrochemical cell having a gel electrolyte |
| CN102903954B (en) * | 2011-07-25 | 2015-06-03 | 微宏动力***（湖州）有限公司 | Lithium ion secondary battery containing ion liquid electrolyte |
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| JPH08295715A (en) * | 1995-04-25 | 1996-11-12 | Nippon Oil Co Ltd | Solid polymer electrolyte |
| JP2013254633A (en) * | 2012-06-06 | 2013-12-19 | Asahi Kasei Corp | Electrolyte for electrochemical device, and lithium ion secondary battery |
| CN104981934A (en) * | 2012-11-12 | 2015-10-14 | 诺莱特科技公司 | Non-aqueous electrolytic solutions and electrochemical cells comprising same |
| CN106797048A (en) * | 2014-10-02 | 2017-05-31 | 株式会社Lg化学 | Gel polymer electrolyte and the lithium secondary battery including the gel polymer electrolyte |
| WO2017179468A1 (en) * | 2016-04-12 | 2017-10-19 | ダイキン工業株式会社 | Electrolyte solution, electrochemical device, lithium ion secondary battery and module |
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| Publication number | Publication date |
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| EP3648230A4 (en) | 2020-05-06 |
| KR102288125B1 (en) | 2021-08-11 |
| KR20190065155A (en) | 2019-06-11 |
| EP3648230B1 (en) | 2022-08-10 |
| EP3648230A1 (en) | 2020-05-06 |
| CN111183544A (en) | 2020-05-19 |
| PL3648230T3 (en) | 2022-10-31 |
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